1. Field of the Invention
The invention herein pertains to the field of herbicides. In more particular the invention pertains to the field of herbicides suitable for use against undesired vegetation in the presence of transplanted rice. In still more particular, this invention pertains to the preemergent or postemergent use of N-(butoxymethyl)-640 -tert-butyl-2-chloro-o-acetotoluidide against monocotyledonous and dicotyledonous weeds, e.g., grasses, sedges and broadleaf weeds, in the presence of transplanted rice.
2. Description of the Prior Art
The food crop rice is the major food staple for approximately 60% of the world's population. This crop is grown on an estimated 326 million acres (about 131.9 million hectares). Of the total rice coverage under cultivation, it is estimated that 70%, or about 229 million acres (about 92.7 million hectares), is the transplanted rice culture, and the remaining 30%, or about 97 million acres (about 39.3 million hectares), is the direct-seeded rice culture (including drill-seeded, broadcastsown, puddle-seeded, water-seeded and upland). Accordingly, much effort is required to produce sufficient rice to meet the widespread demand therefor.
Most of the rice lands under cultivation are weeded by hand, hence, much human effort is expended in raising rice. It has been estimated that to manually remove weeds from transplanted rice fields requires 120-160 man hours per acre (300-400man hours per hectare). Hand-weeding in direct-seeded rice is even more demanding. Thus, with 326 million acres in rice production and the ever-increasing migration of farm workers to the cities, especially in developing countries, rice herbicides are achieving an even greater importance in helping to raise sufficient rice to meet the needs of those dependent upon it.
A number of herbicides have been introduced on the market in an effort to provide chemical weeding of rice fields. However, rice herbicides (i.e., herbicides useful against weeds in rice fields) of the prior art have met with only more or less limited success, because of certain inherent limitations. For example, it is known that the following prior art rice herbicides have the indicated disadvantages: (1) 3,4-dichloropropionanilide has strict requirements as to the method of application and water management; (2) 2-chloro-N-(butoxymethyl)-2',6'-diethylacetanilide, and the chlorinated phenyl nitrophenyl ethers, e.g., 2,4-dichloro- and 2,4,6 -trichlorophenyl-4-nitrophenyl ethers, or a mixture of the latter with p-chlorobenzyl-N,N-diethylthiolcarbamate have only brief periods of application; (3) S-ethyl hexahydro-1H-azepine-1-carbothioate has a narrow spectrum of weed control; and (4) the phenoxies, 2-tert-butyl-4-(2,4-dichloro-5-isopropyloxyphenyl)-5-oxo-1,3,4-oxadiazolin e and mixtures of p-chlorobenzyl-N,N-diethylthiolcarbamate with 2,4-bis (ethylamino)-6-(methylthio)-s-triazine have marginal crop safety. Combinations of the foregoing disadvantages are also found in prior art rice herbicides.
Among herbicidal compounds of the prior art which are most closely related in structure to the compound of interest in the present invention are the N-oxaalkylene-.alpha.-haloacetanilides. Included within these prior art acetanilide compounds are those wherein the positions ortho to the anilide nitrogen atom are both unoccupied by any substituents, or one or both ortho positions are occupied by various radicals including straight or branched-chain alkyl radicals, and the oxaalkylene substituent on the anilide nitrogen atom has one or more carbon atoms in the alkylene moiety adjacent to the nitrogen atom. By "oxaalkylene" is meant an alkylene radical one of whose methylene groups has been replaced with an oxa oxygen atom (--O--) resulting in a radical of the structure --CH.sub.2 --O--CH.sub.2 --.
Illustrative of the .alpha.-haloacetanilide herbicidal compounds of the above types are such compounds as are described in U.S. Pat. Nos. 2,863,752, 3,442,945, 3,547,620, 3,663,200 and British Pat. No. 1,008,851, all of which are assigned to applicant's assignee herein. In said U.S. '752 patent, the ortho positions may be both occupied by hydrogen atoms or one of these positions may be occupied with, inter alia, an alkyl radical having up to four carbon atoms. Said British Pat. No. 1,008,851 discloses N-oxaalkylene compounds wherein one of the ortho positions may be an alkyl group and the other ortho position must be occupied by a tert-alkyl group. Both of said U.S. '752 and British '851patents exemplify the above types of compounds with no less than two alkylene carbon atoms in the oxaalkylene moiety of the compounds. Moreover, neither of the '752 nor '851 patents disclose any herbicidal utility with respect to rice of any culture.
The above U.S. Pat. No. 3,663,200 discloses the use of N-butoxymethyl-2',6'-diethyl-2-chloroacetanilide (common name --butachlor) and/or its N-butoxyethyl homolog as rice herbicides for inhibiting the growth of other grasses, e.g., barnyardgrass. In field tests comparing herbicidal properties of butachlor, the active ingredient of a commercial rice herbicide with those of the compound of the present invention, it was found that the latter is superior to the former in two important aspects, viz. (1) the application rate use requirements are from 3 to 6 (or more) times less, and (2) the time span of application to the weeds is much greater, i.e., the compound of this invention may be effectively applied as late as the 2-2.5 leaf stage of growth, whereas butachlor is applied at the 1 leaf stage of growth to achieve optimum weed control.
Said U.S. Pat. No. 3,663,200 patent is a continuation-in-part of said U.S. Pat. No. 3,547,620 patent. The compound of use in the present invention is also disclosed as a herbicidal compound in said '620, as well as in said '945 patent. It is also disclosed in Table I in each of said '620 and '945 patents that the compound of Example 4 in each of said patents (the same compound of the present invention, but with slightly different nomenclature) was tested for herbicidal activity with respect to a variety of weeds and crops, including "rice". However, the rice plants used in the '620 and '945 patents were direct-seeded rice culture as indicated by the disclosed method of planting and growing the plants. As shown in Table I of each of said '620 and '945 patents, the compound of Example 4 therein exhibited severe phytotoxicity with respect to direct-seeded rice plants under the conditions of the test and at the concentrations used, i.e., 1.0 lb/ac (ca. 1.12kgs/ha) and 0.25 lb/ac (ca. 0.28 kg/ha). Accordingly, that disclosure standing alone would tend to suggest to those skilled in the art that the compound of said Example 4 would be unsatisfactory for use as a rice herbicide, at least, at the rates tested.